Muscle electrolytes in acid and alkaline solutions.

FENN, WALLACE O.,TERENCE A. ROGERSANDELEONORE A. OHR. Muscle etectrdytes in acid and alkaline solutions. Am. J. Physiol. 194(2): 373-378. [email protected] frog muscles were equilibrated in solutions of varying pH and were then analyzed for potassium, sodium and sometimes chloride, phosphate, or bicarbonate. It was found that acid applied outside the muscle causes in most cases an increased loss of K. Over the physiological pH range this was also true of Na in experiments in which the complication of the extracellular space was minimized by replacing 90% of the NaCl of the solution by sucrose. In the other experiments the variations were such that it was impossible to establish any regular effect of pH on the movements of sodium. Except at a pH below 2 or above I 2 the Na did not appear to exchange with K in response to injury. It is suggested that the Na pump in muscle works better when the Na is being moved into a more acid solution. It is concluded that muscle neutralizes external acid in part by loss of K, sometimes by loss of Na, and to some extent by gain of chloride. There was a slightly increased loss of phosphate and bicarbonate from muscle in the more acid solutions but no evidence of an increase in the extracellular fluid as measured by inulin. I T WAS SHOWN by Fenn and Cobb (I) in 1934 that frog skeletal muscles lost increasing amounts of potassium as the pH of the surrounding solution decreased. This could be regarded as a depolarization of the muscle due to the acidity, which resulted in a loss of K; or as an exchange of K for a hydrogen ion. This is the behavior which would be expected if the K were retained inside the muscle by a Donnan membrane equilibrium, with a membrane which was functionally at least impermeable to sodium. Further evidence for such an equilibrium was presented later by Boyle and Conway (2). The present experiments were undertaken to find out whether there actually was in these experiments any exchange of sodium as a result of the pH changes. The answer to this simple question has proved to be remarkably elusive and has required at least 2 years for a reasonably definitive result. The work has involved Received for publication January 16, 1958. 1 Supported in part by a research grant (A-869) from the National Institute of Arthritis and Metabolic Diseases. the efforts of four different assistants engaged on the problem at different times since 1953 and 120 different experiments. The general result has been that lowering the pH from 7.3 to 6.3 causes a loss of potassium; the change of sodium in the same muscles is quite variable and usually not significantly different from zero although in the most reliable experiments there is a consistent but small loss. This might be interpreted as meaning that the sodium pump in muscles operates more effectively when the outside solution is more acid.